since when does caffeine kicking in make you sleepy? one thing you could try doing is buying pills that increase your melantonin. these pills are all natural supplements so you don't have to worry about getting strung out haha. they work well in giving you a good nights sleep. plus, they are cheap!
http://www.melatonin.com/melatonin-faq.htm
http://www.worldwidelabs.com/prod_melat.htm
good luck